This invention relates to technology for rotating a semiconductor wafer during post copper electroplating processing in a post electrofill module. More particularly, the invention pertains to wafer chucks used in such modules to align, rotate and clamp the semiconductor wafer. The modules typically perform a metal etch removing the edge bevel copper, rinse the wafer, and dry the wafer. A post electrofill module is typically a part of an integrated electrofill module that includes metal deposition, etching, and any other pre- and post treatment.
During integrated circuit fabrication, conductive metal is needed on the active circuit region of the wafer, i.e., the main interior region on the front side, but is undesirable elsewhere. In a typical copper Damascene process, the formation of the desired conductive routes generally begins with a thin physical vapor deposition (PVD) of the metal, followed by a thicker electrofill layer (which is formed by electroplating). The PVD process is typically sputtering. In order to maximize the size of the wafer's useable area (sometimes referred to herein as the “active surface region”) and thereby maximize the number of integrated circuits produced per wafer), the electrofilled metal must be deposited to very near the edge of the semiconductor wafer. Thus, it is necessary to allow physical vapor deposition of the metal over the entire front side of the wafer. As a byproduct of this process step, PVD metal typically coats the front edge area outside the active circuit region, as well as the side edge, and to some degree, the backside. Electrofill of the metal is much easier to control, since the electroplating apparatus can be designed to exclude the electroplating solution from undesired areas such as the edge and backside of the wafer. One example of plating apparatus that constrains electroplating solution to the wafer active surface is the SABRE™ clamshell electroplating apparatus available from Novellus Systems, Inc. of San Jose, Calif., aspects of which are described in U.S. Pat. No. 6,156,167, “CLAMSHELL APPARATUS FOR ELECTROCHEMICALLY TREATING SEMICONDUCTOR WAFERS,” which is herein incorporated by reference in its entirety.
The PVD metal remaining on the wafer edge after electrofill is undesirable for various reasons. One reason is that PVD metal layers are thin and tend to flake off during subsequent handling, thus generating undesirable particles. This can be understood as follows. At the front side edge of the wafer, the wafer surface is beveled. Here the PVD layers are not only thin, but also unevenly deposited. Thus, they do not adhere well. Adhesion of subsequent dielectric layers onto such thin metal is also poor, thus introducing the possibility of even more particle generation. By contrast, the PVD metal on the active interior region of the wafer is simply covered with thick, even electrofill metal and planarized by CMP down to the dielectric. This flat surface, which is mostly dielectric, is then covered with a barrier layer substance such as SiN that both adheres well to the dielectric and aids in the adhesion of subsequent layers.
To address these problems, semiconductor equipment may have to allow etching of the unwanted residual metal layers. Various difficulties will be encountered in designing a suitable etching system. One such difficulty involves the design of wafer chucks that hold the semiconductor wafer during the metal etch. First, the system must align the wafer on chuck for rotation. Conventionally, such alignment is done by placing the wafer in a separate alignment module and then transporting it the chuck. Unfortunately, this approach involves a separate alignment step that can add expense and affect IC throughput. Further, the wafer chuck should not contact the wafer edges during the actual etching of unwanted metal from those regions. Otherwise, the viscous etchant would not be able flow over the side edge of the wafer unimpeded. Still further, the chuck should be able to clamp the wafer during acceleration, deceleration and high-speed rotation (e.g., greater than 750 rpm), such as is typically used in drying operations. The chuck must be made of materials that are resistant to the etching properties of the etchant. The chuck should also be designed to facilitate wetting and rinsing operations, and to allow unimpeded application of the etchant to the backside of the wafer.
For these reasons, an improved wafer chuck design is required for etching unwanted metal from semiconductor wafers.